The DVD video format is one of the read-only standards set for DVD (digital versatile disc). With the DVD video format in use, content data such as video and audio data and various kinds of sub picture data such as subtitles are multiplexed into program streams that are recorded to a disc. Also recorded to the disc is navigation data for interactively reproducing the recorded program streams.
Interactive reproduction involves allowing the user to reproduce recorded data by making use of diverse DVD functions. These functions include: the basic function of letting the data be reproduced from any desired positions or in any desired order; a multi-angle function whereby images taken from diverse angles are reproduced; a multi-language function whereby the data is reproduced in any one of a plurality of languages; and a parental control function whereby violent or other undesirable scenes are prevented from getting reproduced.
A plurality of audio streams and a plurality of sub picture streams may be multiplexed into a program stream. This feature makes it possible record on a disc a single video content such as a movie together with a plurality of languages as audio and subtitle data. At the start of or during video reproduction, the user is allowed to select a desired language for audio and subtitle output.
Illustratively, Patent Document 1 discloses a system that allows a user easily to download contents such as sound effects and moving or still images used as materials for video works. Patent Document 2 discloses techniques for replacing certain portions of an integral set of music data with other data.
[Patent Document 1]    Japanese Patent Laid-Open No. 2003-140662
[Patent Document 2]    Japanese Patent Laid-Open No. 2002-311967